The instant invention comprises an improvement over the water tank and outlet valve construction disclosed in my prior U.S. Pat. No. 3,148,381. The basic structure of the instant invention is very similar to the structure of my prior patented tank and outlet valve structure, but the latter does not include means whereby excess water supplied to the interior of the tank through the inlet valve therefor may be discharged therefrom in order to prevent tank overflow. Still further, my previous invention relied solely upon sloped lower supporting surfaces for guiding the valve ball back into seated engagement with the outlet opening upon the flush water being drained from the tank.